Centrifuges are well-known, but to date, centrifuges, particulary those designed to process so-called "micro sample tubes" often called "Eppendorf type tubes", have been so noisy as to preclude working or even holding conversation in their vicinity when they are in operation. This highly undesirable noise is generated primarily by the circular array of sample tubes spinning exposed to the air stream at angular velocities in the range of ten thousand to sixteen thousand revolutions per minute with sample tube tip velocities in the range of two hundred twelve to three hundred thirty-nine feet per second. Still another source of such noise is the characteristic whine of the high-speed, brush-type electric motor used in centrifuges. High-speed, brush-type electric motors are inherently noisy with a characteristic high-pitched whine caused by the carbon brushes riding on the segmented surface of the commutator.
To lessen the primary cause of noise, it has been known to enclose the lower portions of the sample tubes within a monolithic or fabricated body sometimes referred to as a "windshield". Although this does help, the filler neck of each tube still remains exposed to the air, thereby still generating considerable undesirable noise.
Corrosive damage is still another problem with known centrifuges, particulary those of the fixed angle design which is the most popular design. So-called "fixed angle" designs carry the sample tube or container rigidly with the major axis of the sample tube disposed typically but not necessarily at thirty degrees to forty-five degrees from the vertical or spin axis. Sample tube receptacles are typically formed by boring holes in a monolithic body, often termed a "rotor". Non-monolithic rotor configurations are also known where tube receptacles are otherwise provided by a structure which is permanently assembled into such a rotor.
It is in the tube receptacles where hidden corrosion begins when a sample tube ruptures thereby allowing the possibly corrosive contents of the sample tube to become trapped in the blind tube receptacles.
Still another disadvantage of known drive assemblies for centrifuges is that there is either no braking or only ineffective braking, which braking becomes progressively less effective as zero speed is approached, resulting in wasted time and an undesirably long exposure of test samples to elevated temperatures.
Centrifuge devices usually have some means to protect the operator from possible injury caused by inadvertent contact with a spinning rotor. Some of the most advanced centrifuges interlock the rotor chamber access door to prevent the access door from being opened when the rotor is turning. However, the means for detecting motion of the rotor could fail or be sufficiently imprecise that the access door could be opened on a spinning rotor. Still another disadvantage of some existing interlock systems is failure of the interlock system in the event of a power interruption, after the rotor has attained considerable angular velocity.
Often it is necessary to perform a very short run or spin with a centrifuge. The duration of such a short spin is typically 10-30 seconds, which until this invention was too short for interval timers of the type normally applied to accommodate.
Still another disadvantage of the centrifuge known in the art is undesirable variations of centrifugal force exerted on the sample due to variations in the speed of rotation and the fact that centrifugal force on a particle in a sample tube varies as the square of the speed of rotation of the rotor.
Still another disadvantage with the present art is contamination when a sample tube containing radioactive or biohazardous material ruptures during processing. Some designs do use a fully-enclosed rotor so that the liquid would be contained within the rotor if spilled. Even with these units, the rotor cover must be removed in order to remove the rotor body and the sample tubes contained therein, thereby allowing contaminants to escape. Therefore, with the current state of the art, the usual way to remove the hazardous material is to place the entire centrifuge in a ventilated hood for rotor access and cleanup which is extremely inconvenient and cumbersome.
Still another disadvantage of those existing centrifuges which offer effective-braking means is failure to provide a gentle approach to the zero speed state. An excessive rate of deceleration, if maintained to the actual instant of stopping, can cause undesirable agitation and re-suspension of certain unstable and non-compacted "pellets" in the test material.